1. Technical Field
The present invention relates to a method and system for presence detection within a predetermined detection volume using an arrangement for transmitting and receiving microwave radiation.
2. Background Art
Systems for detection of the presence humans, animals, and other objects in a defined area or space are well-known and are commonly used, for example as intrusion detection systems. With regard to vehicles, for example, it is common today to use intrusion detectors in order to provide an alarm in the event that the presence of a human or an animal is detected within the passenger compartment of the vehicle.
A system for presence detection in a vehicle may comprise a combined radio transmitter and receiver based on microwave technology, which means that the radio transmitter is arranged for emitting microwave radiation into a space corresponding to the vehicle's passenger compartment. Furthermore, the receiver is arranged for detecting any microwave radiation which is reflected as a result of humans, animals, or other moving objects being present in the space. In order to achieve this, it is previously known to use microwave-based detection units of the so-called Doppler motion sensor type. Such units are based on the Doppler shift phenomenon in order to detect motion of objects in a space.
U.S. Pat. No. 6,426,716 teaches a motion sensor based on a microwave transceiver apparatus. Furthermore, patent document EP 213558 teaches an intrusion detection device based on microwave technology, wherein an oscillator which is used to generate microwave radiation also is used as a detector.
In the field of intrusion detection, it is sometimes important that intrusion only be detected in a very well-defined space, i.e. corresponding to a well-defined distance from the detector. This means that the components used, in particular the microwave transmitter and receiver, must be very accurate and of high quality so that the detection volume can be defined in an exact manner within the vehicle. Otherwise, there will be a risk for false alarms if for example a person or animal passes just outside of the detection volume. Consequently, there is a demand for improved systems arranged for precisely regulating the detection boundaries around an intrusion detector—which means that false alarms can be minimized or preferably eliminated—while still using components and circuit solutions at a relatively low cost.